<p>The PP-loop motif appears to be a modified version of the P-loop of nucleotide binding domain that is involved in phosphate binding [<cite idref="PUB00014303"/>]. Named PP-motif, since it appears to be a part of a previously uncharacterised ATP pyrophophatase domain. ATP sulfurylases, <taxon tax_id="562">Escherichia coli</taxon> NtrL, and <taxon tax_id="1423">Bacillus subtilis</taxon> OutB consist of this domain alone. In other proteins, the pyrophosphatase domain is associated with amidotransferase domains (type I or type II), a putative citrulline-aspartate ligase domain or a nitrilase/amidase domain.</p><p>PP-loop ATPases are part of the HUP domain class (after HIGH-signature proteins, UspA, and PP-ATPase), along with the nucleotide-binding domains of class I aminoacyl-tRNA synthetases, UspA protein (USPA domains), photolyases, and electron transport flavoproteins (ETFP). The HUP domain is a distinct class of alpha/beta domain [<cite idref="PUB00016132"/>].</p><p>This entry represents MJ1599-type predicted PP-loop ATPases. </p> ATPase, PP-loop, MJ1599-related